Ulrich Englich

CALCIUM, STRONTIUM, AND BARIUM ACETYLIDES : NEW EVIDENCE FOR BENDING IN THE STRUCTURES OF HEAVY ALKALINE EARTH METAL DERIVATIVES

An unprecedented ligand bending mode is displayed by the acetylide ligands in the first structurally characterized σ-bound organometallic strontium and barium complexes [M([18]crown-6)(CCSiPh3 )2 ] (M=Sr, Ba). Furthermore, the observed decrease of the angle at the sp-hybridized C atom on descending Group 2 (see structures depicted) affords new information that will lead to a better understanding of the bonding in alkaline earth metal compounds.

Thiolates, selenolates, and tellurolates of the s-block elements

Abstract The potential of alkali and alkaline earth metal chalcogenolates in synthetic chemistry and various technical applications has sparked the recent interest in the chemistry of alkali and alkaline earth metal thiolates, selenolates and tellurolates. As a result, an increasing body of work concerned with exploring synthetic routes to the target compounds, analyzing the influence of metal, ligand and donor on the structural chemistry, and correlating structure and function has appeared in the literature, most of which during the last few years. This article describes recent trends in this area of alkali and alkaline earth chemistry, by discussing synthetic access routes, analyzing structure determining factors such as metal, donor and ligand influence, comparing structural similarities and disparities in alkali and alkaline earth chemistry, and discussing structure–function relationships.

Reaction pathways towards 1,1,2,2-tetratbutyldistannanes

Abstract 1,2-Dichlorotetratbutyldistannane (1) is synthesized as a byproduct in the reaction of tbutylmagnesium chloride with tin tetrachloride or by the reaction of ditbutyltindihydride with ditbutyltin dichloride in the presence of amines. Reaction of 1 with lithium aluminumhydride yielded the dihydrido derivative 2. The treatment of 2 with bromoform gave the dibromo distannane 3 nearly quantitatively. Reactions of 2 with one equivalent of LDA or KH yielded unsymmetrically substituted alkali metal distannanes of the type MtBu2SnSn(H)tBu2 (4, M=Li; 5, M=K). Reaction of either two equivalents of KH with 2, or one equivalent of KH with 5 gave the dipotassium distannide 6. The molecular structure of the dichloro derivative 1 was determined by X-ray diffraction.

Novel triphenyltin substituted derivatives of heavier alkaline earth metals

Abstract The synthesis and characterization of a family of novel alkaline earth metal stannides, in addition to tri- and pentastannanes are described. [Ba(18-crown-6)(HMPA) 2 ][SnPh 3 ] 2 ( 4 ), [Ca(18-crown-6)(HMPA) 2 ][Sn(SnPh 3 ) 3 ] 2 ( 5 ), and [Sr(18-crown-6)(HMPA) 2 ][Sn(SnPh 3 ) 3 ] 2 ( 6 ) were synthesized by insertion of the corresponding alkaline earth metals into the tintin bond of hexaphenyldistannane. Ph 3 SnSnPh 2 SnPh 3 ( 7 ), and Sn(SnPh 3 ) 4 ( 8 ) became available by treating 4 with diphenyldichlorostannane. All compounds were studied by NMR spectroscopy, and X-ray crystallography. The stannanes 7 and 8 were also characterized by elemental analysis.

Calcium-, Strontium- und Bariumacetylid – neue Befunde für die gewinkelte Struktur von Derivaten der schweren Erdalkalimetalle

Abgewinkelt koordiniert sind die Acetylidliganden in den ersten strukturell charakterisierten metallorganischen Erdalkalimetallverbindungen [M([18]Krone-6)(CCSiPh3)2] (M=Sr und Ba), die Metall-C-σ-Bindungen aufweisen. Die daruber hinaus beobachtete Abnahme des Winkels am sp-hybridisierten C-Atom beim Gang zu den schweren Elementen (siehe Strukturen im Bild) liefert neue Ansatze fur ein tieferes Verstandnis der Bindungsverhaltnisse in Erdalkalimetallverbindungen.

Can radiation damage to protein crystals be reduced using small-molecule compounds?

Recent studies have defined a data-collection protocol and a metric that provide a robust measure of global radiation damage to protein crystals. Using this protocol and metric, 19 small-molecule compounds (introduced either by cocrystallization or soaking) were evaluated for their ability to protect lysozyme crystals from radiation damage. The compounds were selected based upon their ability to interact with radiolytic products (e.g. hydrated electrons, hydrogen, hydroxyl and perhydroxyl radicals) and/or their efficacy in protecting biological molecules from radiation damage in dilute aqueous solutions. At room temperature, 12 compounds had no effect and six had a sensitizing effect on global damage. Only one compound, sodium nitrate, appeared to extend crystal lifetimes, but not in all proteins and only by a factor of two or less. No compound provided protection at T=100 K. Scavengers are ineffective in protecting protein crystals from global damage because a large fraction of primary X-ray-induced excitations are generated in and/or directly attack the protein and because the ratio of scavenger molecules to protein molecules is too small to provide appreciable competitive protection. The same reactivity that makes some scavengers effective radioprotectors in protein solutions may explain their sensitizing effect in the protein-dense environment of a crystal. A more productive focus for future efforts may be to identify and eliminate sensitizing compounds from crystallization solutions.

Barium thiolates and selenolates: Syntheses and structural principles

The synthesis and structural characterization of a family of barium thiolates and selenolates is described. The thiolates were synthesized by metallation of thiols, the selenolates by reductive insertion of the metal into the selenium-selenium bond of diorganodiselenides. Both reaction sequences were carried out by using barium metal dissolved in ammonia; this afforded barium thiolates and selenolates in good yield and purity. The structural principles displayed in the target compounds span a wide range of solid-state formulations, including monomeric and dimeric species, and separated ion triples, namely [Ba(thf)4(SMes*)2] (1; Mes* = 2,4,6-tBU3C6H2), [Ba(thf)4(SeMes*)2] (2), [Ba([18]crown-6)(hmpa)2][(SeMes*)2] (3), the dimeric [(Ba(py)3(thf)(SeTrip)2)2] (4; py = pyridine, Trip = 2,4.6-iPr3C6H2), and [Ba([18]crown-6)(SeTrip)2] (5). The full range of association modes is completed by [Ba([18]crown-6)(hmpa)SMes*][SMes*] (6) communicated earlier by this group. In the solid state, this compound displays an intermediate ion coordination mode: one anion is bound to the metal, while the second one is unassociated. Together these compounds provide structural information about all three different association modes for alkaline earth metal derivatives. This collection of structural data allows important conclusions about the influence of solvation and ligation on structural trends.

Core Modified meso‐Aryl Corrole: First Examples of CuII, NiII, CoII and RhI Complexes

A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the alpha-alpha coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Nil(II), Cu(II), and Co(II) with the participation of all heteroatoms in the coordination. However, Rh(I) ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni(II) and Rh(I) complexes reveal square planar geometry completed by two CO molecules for Rh(I). The EPR spectra of the paramagnetic that Cu(II) and Col(II) complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the Cu(II) complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO.

When VSEPR Fails: Experimental and Theoretical Investigations of the Behavior of Alkaline‐Earth‐Metal Acetylides

The synthesis, structural, and spectral characterization as well as a theoretical study of a family of alkaline-earth-metal acetylides provides insights into synthetic access and the structural and bonding characteristics of this group of highly reactive compounds. Based on our earlier communication that reported unusual geometry for a family of triphenylsilyl-substituted alkaline-earth-metal acetylides, we herein present our studies on an expanded family of target derivatives, providing experimental and theoretical data to offer new insights into the intensively debated theme of structural chemistry in heavy alkaline-earth-metal chemistry.

A Novel Beryllium Thiolate Resulting from N−Si Bond Cleavage: Liberation of Ammonia in the Reaction of Be[N(SiMe3)2]2 with HSPh

A side reaction leads to the product. In the synthesis of [{Be(SPh)2 (py)(NH3 )}2 {[18]crown-6}] (1, py=pyridine) from [Be{N(SiMe3 )2 }2 ] and HSPh, the coordinated ammonia molecules (see the structure of 1 in the picture) are formed in a competing reaction between liberated hexamethyldisilazane and the thiol.